Conventional utility networks supply utilities for commercial, residential and industrial purposes. In a typical electrical distribution system, for example, electrical energy is generated by an electrical supplier or utility company and distributed to consumers via a power distribution network. The power distribution network is often a network of electrical distribution wires (more commonly known as “electrical transmission lines”) which link the electrical supplier to its consumers. Additional devices, such as bus bars, switches (e.g., breakers or disconnectors), power transformers, and instrument transformers, which are typically arranged in switch yards and/or bays, are automated for controlling, protecting, measuring, and monitoring of substations.
Typically, electricity from a power utility is fed from a primary station over a distribution cable to several local substations. At the local substations, the supply is transformed by distribution transformers from a relatively high voltage on the distributor cable to a lower voltage at which it is supplied to the end consumer. From the local substations, the power is provided to industrial users over a distributed power network that supplies power to various loads. Such loads may include, for example, various power machines, lighting, HVAC systems, etc.
In general, the power factor of a multi-phase alternating current (AC) electric power system is the ratio of the real (or “active”) power used in a circuit to the apparent power used by the circuit. Real power, which is typically expressed in watts (W) or kilowatts (kW), is the capacity of the circuit for performing work in a particular time, whereas apparent power, which is typically expressed in volt-ampere (VA) or kilo volt-ampere (kVA), is the product of the current and voltage of the circuit. Power factor correction (PFC) can be achieved, for example, by switching in or out banks (or racks) of capacitors. A capacitor bank is typically composed of a number of discrete steps that can be switched in and out of operation. Each step is composed of a number of individual low-inductance capacitors that are wired in parallel (or series, depending upon the system), and sum together to provide the total capacitance for the step. In general, capacitor banks act to maintain a relatively constant power factor over a particular site or a portion of an electric distribution system to maximize the real power transfer capacity of the conductors and minimize the loses of the electric distribution system.
Power capacitors are naturally prone to aging effects that can change their electrical characteristics (e.g., capacitance, internal resistance, etc.), which in turn can reduce their effectiveness. Depending on the constituent materials, the design type, and the details of manufacturing, for example, some capacitors may be prone to different types of failure if their electrical characteristics change at a faster rate than expected from normal aging. In some cases, these failures can be mitigated by a self-protection mechanism, which is activated, for example, by overpressure, overtemperature, and/or overcurrent to responsively remove the capacitor from the circuit. Other cases may lead to a failure where the self-protection mechanism does not to operate properly.
It is common today for capacitor bank installations to have very limited or no monitoring and diagnostics available, due in part to limited available packaging space within the capacitor bank cabinet (or “locker”) and the expense associated with monitoring the individual capacitors in a capacitor bank. As a result of this limited monitoring and diagnostics, it is very difficult to detect operational problems before they occur in order to mitigate operational concerns and minimize service disruption through regular maintenance efforts. However, in some applications, the use of sensors placed in intimate contact with a surface of the device being monitored can provide valuable information, e.g., for monitoring temperature, vibration, or deformation, that can be used, for example, to anticipate future problems. Consequently, there is a need for systems, methods and devices for monitoring temperature, vibration, and/or deformation in a capacitor bank.